In the general type of core-manufacturing method that we are concerned with, magnetic strip material is wrapped in superposed relationship about the window of the core to build up a core form, and the core form is later annealed at elevated temperature to relieve stresses therein. A problem that arises in such manufacture is that the heat of the annealing operation often produces, within the core, regions where juxtaposed sections of strip adhere together and form relatively low resistance paths, or shorts, between the adhering strip sections. Such internal adhesions or shorts are undesirable because they can produce within the core, transversely of the flux path therethrough, low-resistance closed circuits for eddy currents; and such closed circuits have the detrimental effect of reducing the effective net cross-section of the core, the amount of such reduction being a direct function of the cross-sectional core area bounded by such closed circuit or circuits.
In the manufacture of cores from traditional silicon-iron strip material, one approach that has been used for reducing the number of such internal shorts is to sharply strike the outer periphery of the annealed silicon-iron core form with a mallet or the like, thereby creating impacts which disrupt the adhesions forming the shorts. This approach has limited utility in the manufacture of amorphous metal cores because the amorphous steel strip material from which the core is formed is very brittle, especially after annealing, and is highly susceptible at this time to being cracked or shattered by any vigorous impacts delivered to the core. Another complicating factor with respect to cores of amorphous steel strip is that the strip material used in such cores typically has no insulating coating applied to it, and this increases the chances for developing metal-to-metal adhesions between juxtaposed sections of strip during annealing, as compared to the situation present with traditional silicon-iron strip, which typically has an insulating coating applied to it.
Another factor which tends to increase the chances for developing metal-to-metal adhesions between the juxtaposed strip sections of amorphous metal cores is that the amorphous strip material typically has surface irregularities on one side, much more pronounced than are present in traditional silicon-iron strip material, where both surfaces are relatively smooth. These surface irregularities result in the presence of small protrusions having peaks that tend to adhere to the juxtaposed strip material, especially when subjected to heat and pressure during annealing.